Annales Societatis Geologorum Poloniae (2016), vol. 86: 355–377. doi: https://doi.org/10.14241/asgp.2016.008 PRESSURE DISSOLUTION FEATURES IN OXFORDIAN MICROBIAL-SPONGE BUILDUPS WITH PSEUDONODULAR TEXTURE, KRAKÓW UPLAND, POLAND Jacek MATYSZKIEWICZ & Alicja KOCHMAN AGH University of Science and Technology, Faculty of Geology, Geophysics and Environment Protection, al. Mickiewicza 30; 30-059 Kraków, Poland; e-mails: [email protected]; [email protected] Matyszkiewicz, J. & Kochman, A., 2016. Pressure dissolution features in Oxfordian microbial-sponge buildups with pseudonodular texture, Kraków Upland, Poland. Annales Societatis Geologorum Poloniae, 86: 355–377. Abstract: Part of the Oxfordian carbonate buildups in the southern part of the Kraków Upland is developed as pseudonodular limestones, which represent segment reefs. These limestones are composed of connected, roun- ded-oval to subangular carbonate pseudonodules. The pseudonodules, densely packed within the limestone, fall out easily under mechanical stress. The recently observed texture of pseudonodular limestones resulted from two stages of chemical compaction. During the first stage, in the Late Jurassic, high-amplitude and low-amplitude stylolites and dissolution seams were formed. The sites particularly favourable for the development of high-amplitude stylolites were the boun- daries between already lithified fragments of the laminar, rigid microbial-sponge framework. The low-amplitude stylolites formed mainly in the intercalated wackestone-packstone, which was lithified somewhat later; hence, the dissolution seams originated at the contacts between the rigid microbial-sponge framework and the wackestone- packstone. After Early Cretaceous erosion, which decreased the burial load, Late Cretaceous sedimentation enabled the renewal of pressure dissolution. Thus, some low-amplitude stylolites evolved into dissolution seams. In stylolites composed of both low- and high-amplitude segments, dissolution proceeded at the bases of interpenetrating high-amplitude stylolite columns, with the simultaneous transformation of low-amplitude stylolite segments into dissolution seams. These seams, which formed at the initial stage of chemical compaction, were subjected in turn to further pressure dissolution, giving rise to the formation of horsetail structures. The vertical stress field, which triggered the pressure dissolution processes, presumably resulted in the formation of high-angle and vertical incipient tension gashes. At the beginning of the processes, these gashes remained closed. In the Cenozoic, under the extensional regime generated by overthrusting Carpathian flysch nappes, some high-angle and vertical dissolution seams and low-amplitude stylolites opened up, forming defor- med dissolution seams and deformed stylolites. Under the same conditions, the high-angle and vertical tension gashes opened up as well. Subsequently, during the exposure period, unloading fractures developed, partly as a result of the opening of some subhorizontal and horizontal dissolution seams and stylolites. The unloading fractures, along with the already existing vertical and high-angle tension gashes, formed the network changing the limestone into pseudo- nodules of various shapes and sizes. The open spaces between the limestone fragments became local conduits for karst waters. Key words: Pressure dissolution features, pseudonodularity, microbial-sponge buildups, Oxfordian, southern Poland. Manuscript received 9 December 2015, accepted 16 May 2016 INTRODUCTION Pseudonodular limestone is defined as a rock composed densely packed within the limestone, falling out easily un- of densely packed, connected rounded-oval to subangular der mechanically induced stress. carbonate nodules (e.g., Hummel, 1960; Clari et al., 1984; Pseudonodular (Polish: zrostkowe) limestones are a pe- Dromart, 1989; Matyszkiewicz, 1994, 1997; Martire, 1996; culiar facies of the Upper Jurassic carbonates, common in Clari and Martire, 1996; Marok and Reolid, 2012). The the southern part of the Kraków Upland, in the Mników area boundaries between nodules are indistinct. The nodules are (Fig. 1). Spectacular exposures of pseudonodular limesto- 356 J. MATYSZKIEWICZ & A. KOCHMAN Fig. 1. Location of the Zimny Dó³ Nature Reserve superimposed on a geologic bedrock map after Gradziñski (2009). nes are known from the Zimny Dó³ Valley, near the village fects of bottom currents and later diagenetic transforma- of Czu³ów (Fig. 2). In 1991, thanks to the efforts of Profes- tions. In his interpretations, the currents removed some of sor Ryszard Gradziñski, an abiotic nature reserve was estab- the unlithified carbonate mud and supplied larger fossils, lished there. mostly small ammonites, siliceous sponges and brachio- The origin of the pseudonodular limestones of the Zimny pods. After deposition, diagenetic processes caused the re- Dó³ Valley was discussed by D¿u³yñski (1952) and Matysz- distribution of calcium carbonate, which accumulated kiewicz (1994, 1997) and also noted by Gradziñski (1972), around the fossils and formed concretions, enveloped in the Gradziñski and Bary³a (1986, 2005), and Gradziñski and sediment that was richer in clay. Musielewicz-Jasiñska (1992). Matyszkiewicz (1994, 1997) excluded the action of The pseudonodular limestones of the Mników area bottom currents; as the formative process of the pseudono- were described for the first time by D¿u³yñski (1952), who dular limestones, he proposed chemical compaction, affect- interpreted their origin as resulting from the combined ef- ing the inhomogeneous sediment, composed mostly of mi- PRESSURE DISSOLUTION FEATURES 357 Fig. 2. Sketch of Upper Jurassic tors in the Zimny Dó³ Nature Reserve (after Gradziñski and Bary³a, 2005) with location of pseudonodular limestones exposures. Points marked as A, B, and eastern and western corridors are outcrops described in detail. crobialites and calcified siliceous sponges, in which an ini- from an extension regime generated in the Cenozoic by tial, laminar rigid framework had developed (cf. Pratt, 1982). overthrusting Carpathian nappes, although their formation Furthermore, the principal role in the formation of the already had been initiated in the Late Jurassic or even earlier pseudonodular limestones was played by pressure dissolution (Matyszkiewicz, 1996; Zió³kowski, 2007; Krajewski et al., processes, which generated numerous pressure dissolution 2011). features (PDFs), separating the pseudonodules. During later The Zimny Dó³ Valley is located in the southern part of diagenetic stages, some PDFs were transformed owing to the the Kraków Upland, in the Tenczynek Horst, which borders combined action of solutions circulating within the rock for- on the Krzeszowice Graben to the south (Fig. 1). As a land- mation, karstification, and other weathering processes. form, the Zimny Dó³ Valley developed in the Palaeogene The paper below presents the development of pressure and was covered with loess in the Pleistocene (Gradziñski, dissolution features (PDFs) along with a detailed recon- 1962; D¿u³yñski et al., 1968). Among the typical morpho- struction of the processes, which led to the formation of re- logical features of the Zimny Dó³ area are suffosion sink- cently observed textures of the pseudonodular limestones. holes, the walls of which are composed of loess and the bot- toms of which are Upper Jurassic limestones. These sink- holes originated from the washing of the loess caprock into AREA OF STUDY karst conduits that were present in the Upper Jurassic bed- rock (Gradziñski, 1962; Gradziñski and Bary³a, 2005). The Kraków Upland is located in the area of the Sile- The group of Upper Jurassic tors exposed in the nature sian–Kraków Homocline. Its southern part is cut by numer- preserve is characterised by numerous rectilinear passages ous tectonic horsts and grabens (Fig. 1), resulting mostly (‘corridors’), several metres wide and with vertical rock 358 J. MATYSZKIEWICZ & A. KOCHMAN walls towering on either side (Fig. 2), formed when joint fractures were pulled apart by mass movements (Gradziñski and Bary³a, 2005). In the upper part of the limestone com- plex, one can observe particularly spectacular corridors with vertical walls, composed of pseudonodular limestones. Typical features of the tors are basal niches with overhang- ing ‘eaves’, presumably the effects of karstification of the pseudonodular limestones in conjunction with other weath- ering processes (Gradziñski and Bary³a, 2005). The Upper Jurassic strata of the Mników area attain a maximum thickness of about 130 m, whereas those in the Zimny Dó³ Valley are only 50–80 m thick (Gradziñski and Bary³a, 2005). The exposed limestones (Fig. 3) belong to the Transversarium-Bifurcatus ammonite zones (Matysz- kiewicz, 1994), corresponding to the middle/upper Oxfor- dian break (cf. Matyja and Wierzbowski, 2004). In the na- ture reserve, the Upper Jurassic limestone complex is about 40 m thick. In the eastern part of the reserve, the lower por- tion of the complex is dominated by a massive facies with local lenses of pseudonodular limestones. Pseudonodular limestones dominate in the western part of the reserve, in the upper part of the stratigraphic sequen- ce, above an elevation of 325 m a.s.l. (Fig. 2). Here, hori- zontal layers of pseudonodular limestones, several metres thick, rest upon massive limestones; horizons, nest-like bodies and lenses of pseudonodular limestones are enclosed within the massive facies. TERMINOLOGY Prior to the petrographic characterisation of the